Propylene glycol can be produced by the catalytic hydrogenolysis of sugar alcohols. Commercially, propylene glycol is produced from glycerol. The hydrogenolysis reaction is effectuated by catalysts such as those described in US Patent Application Publication 2009/0088317.
The hydrogenolysis reaction used to create propylene glycol results in the production of side products such as ethylene glycol, 2,3-butanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-pentanediol, and 2,4-pentanediol. However, these diols and the ethylene glycol are difficult to separate from the propylene glycol, and one isomer of the 2,3-pentanediol cannot be economically separated from propylene glycol by distillation. While it is possible to reduce the production of such diols by varying the hydrogenolysis reactions, such variances may reduce the overall productivity of the propylene glycol process.
Methods have been developed to isolate or purify the propylene glycol from these diols and/or the ethylene glycol. U.S. Pat. No. 8,143,458, assigned to Archer-Daniels-Midland Company, discloses processes for producing propylene glycol and separating the unwanted diols from the propylene glycol. While such processes are able to effectively separate the diols from the propylene glycol, such processes are time consuming and expensive.
Thus, needs exist for the more efficient production of propylene glycol from sugar alcohols.